1. Field of Invention
The inventive subject matter relates to a method of utilizing EEG imaging for detection of marker of motion sickness. The inventive subject matter also relates to a method for the discrimination of individuals likely to be susceptible to motion sickness and to a method to evaluate the efficacy of therapeutic interventions aimed at preventing or mitigating motion sickness.
2. Background Art
An objective method for the determination of motion sickness is of importance in evaluating predisposition of individuals to motion sickness in occupations such as aircraft pilots, shipboard personnel. Evaluating onset of motion is also vital in evaluating pharmaceuticals aimed at mitigating the physical effects of motion sickness and at assessing contraindications of new drugs. Additionally, the design of vehicles and motion simulators requires objective measures, verses self-reporting, of motion sickness.
Physiological markers of motion sickness include increase in skin conductance, gastric EEG (gastric tachyarrhythmia) and pallor. EEG markers for motion sickness, however, are unique among markers of motions sickness. Measuring markers of motion sickness by older EEG technologies suffered from poor resolution.
Human brain imaging techniques such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have dramatically increased our knowledge about neural activity related to cognitive and emotional processes (Ferrari, et al, 2004; Hoshi, 2003). fMRI, in particular, is reliable, safe and now gives very high resolution measures of neural activity. However, these brain imaging techniques have a number of disadvantages and limitations, including the fact that they are expensive, non-portable, confine participants to restricted positions, can involve considerable patient or equipment preparation times and involve moderate risk such as exposing people to potentially harmful materials (PET) or loud noises (fMRI)(Ferrari, et al, 2004; Jasdzewsk et al, 2003). An important disadvantage of PET and MRI imaging techniques, however, is that they are not suitable for many uses, including the continuous monitoring and identification of functional brain activation related to cognitive activity and ongoing operator states in natural environments.
New developments in miniaturization make current electro-encephalography (EEG) systems highly operable and reliable. In particular, the two advances of placing the amplifier directly on the electrode and new mathematical techniques for data analysis make EEG much more suitable than previous iterations. The miniature amplifiers provide large signal to noise rations and the analytic techniques bring out signals of interest.
Non-invasive optical methods, such as the use of functional near-infrared spectroscopy (fNIRS) have increasingly been used to investigate functional activation of the human cortex by mapping cortical oxygenation changes (Hoshi, 2003; Obrig and Villringer, 2003). When compared to brain imaging techniques such as MRI and PET, fNIRS is a low cost, low risk, negligibly invasive and portable technology. This makes fNIRS suitable for the study of cerebral changes under many real world conditions (e.g. filed studies, computer operation) and situations requiring continuous monitoring, repeated sessions, or the monitoring of infants and children. Another advantage of fNIRS is that it can be used in conjunction with other brain imaging technologies such as EEG (Obrig and Villringer, 2003) or PET (Villringer, et al, 1997). Combining EEG and fNIR technologies together may enable investigations of the coupling between neuronal and vascular responses to functional brain activation. The ease of application of fNIR compared to EEG makes fNIRS advantageous for use in monitoring operators.
While there is a relative paucity of research on EEG changes associated with motion sickness, several studies have been conducted. Chelen, et al used precoriolis stimulation through to imminent emesis and found that several EEG changes occurred in the temperofrontal region when compared with baseline. These changes included an increase in the mean power spectral energy in the delta band (0-2 Hz) during sickness by a factor of 13.7 and mean theta (3-7 HZ) increases by a factor of 2.2. Chelen and associates reported that these changes also correlated with the level of self-reported MS symptoms. They asserted that these changes (particularly delta band changes) indicate that low frequency oscillatory stimulation is being diffusely projected about the central nervous system.
Hu, et al compared a variety of physiological measures associated with MS, including gastric, myoelectric, electrodermal, cardiovascular and brain electrical activities. While they reported an increase in 4-9 cpm activity (gastric tachyarrhythmia) was the most sensitive physiological index of the severity of motion sickness symptoms, significant increases in EEG activity of the 0.5 to 4 Hz frequency band (delta) also occurred.
Dornhoffer, et al studied Sopite syndrome, a syndrome commonly associated with motion sickness that is characterized by a loss of initiative, sensitivity to normally innocuous sensory stimuli, and impaired concentration amounting to a sensory gating deficit. They used a rotary chair to elicit the sensory mismatch that occurs during motion sickness by over stimulating the vestibular apparatus and measured the effects of rotation on the manifestation of the P50 midlatency auditory-evoked response as a measure of arousal and distractibility. They found that rotation-induced motion sickness produced no change in the level of arousal but did produce a significant deficit in sensory gating. This indicates that some of the attentional and cognitive deficits observed with motion sickness may be due to distractibility induced by decreased habituation to repetitive stimuli.
De Metz, et al found that Fast Fourier analysis of the EEG activity showed more asymmetry between the two hemispheres in subjects who suffered MS as compared with those who did not experience motion sickness. In another study, Min, et al. evoked simulator sickness using a graphic simulator while monitoring EEG. They found that scores on a Simulator Sickness Questionnaire (SSQ) correlated positively with delta/total, and negatively with theta/alpha and beta/total. SSQ scores also had significantly high negative correlations with theta total at both Fz and Cz.
Taken together, the earlier studies do not represent a uniformity of findings for EEG changes associated with motion sickness and may include a wide variety of artifacts. The lack of consistent observations as a predictor of a propensity toward motion sickness was the motivation behind the search for a more reliable methodology, which is an aspect of the current invention